Method for producing purified 2-cyanoacrylate

ABSTRACT

A method for producing a purified 2-cyanoacrylate is characterized in that distillation is conducted in the presence of a polymerization inhibitor whose boiling point is within ±12° C. of the boiling point of the 2-cyanoacrylate. With this method, polymerization of 2-cyanoacrylate can be continuously prevented in the distillate system during distillation of a crude 2-cyanoacrylate, so that a purified 2-cyanoacrylate can be obtained.

TECHNICAL FIELD

The present invention relates to a method for producing a purified2-cyanoacrylate, which is widely used as a main component of an instantadhesive and, in particular, to an improvement in a purification step ofthe production process.

BACKGROUND ART

A 2-cyanoacrylate is generally produced by condensation of acyanoacetate and formaldehyde in an organic solvent, followed bydepolymerization of the polymer thus obtained at high temperature andreduced pressure. A crude 2-cyanoacrylate obtained here generally haslow purity, poor adhesion performance, poor stability, etc., and it istherefore further distilled to give a purified 2-cyanoacrylate.

With regard to distillation and purification of a 2-cyanoacrylate, amethod is known in which, in order to prevent polymerization of the2-cyanoacrylate, an anionic polymerization inhibitor such asdiphosphorus pentoxide, phosphoric acid, or paratoluenesulfonic acid,and a radical polymerization inhibitor such as hydroquinone, catechol,or pyrogallol are added to a crude 2-cyanoacrylate, which is thensubjected to distillation at reduced pressure while heating.

Furthermore, JP-A-1-135754 (JP-A denotes a Japanese unexamined patentapplication publication) proposes a method in which distillation iscarried out while continuously and countercurrently adding apolymerization inhibitor from an upper part of a distillation column.

Moreover, U.S. Pat. No. 2,794,788 discloses a method in whichdistillation is carried out under a flow of an acidic gas such as SO₂,BF₃, HF, or CO₂, for the purpose of inhibiting polymerization of a2-cyanoacrylate in a distillate system.

Furthermore, JP-A4-124168 proposes a method in which distillation iscarried out without using the above-mentioned acidic gas but insteadusing a polymerization inhibitor such as a BF₃ ether complex salt or aBF₃ carboxylic acid complex salt.

DISCLOSURE OF INVENTION

However, even if the above-mentioned polymerization inhibitor such asdiphosphorus pentoxide or hydroquinone, or the polymerization inhibitorsuch as a BF₃ ether complex salt or a BF₃ carboxylic acid complex saltis used, there is still the problem that the 2-cyanoacrylate easilypolymerizes in the distillate system.

Furthermore, with regard to the method in which distillation is carriedout under a flow of an acidic gas such as SO₂, BF₃, HF, or CO₂, since a2-cyanoacrylate thus obtained contains a large amount of acidic gas, itis necessary to remove this acidic gas by degassing, etc. Moreover,since these acidic gases are discharged as exhaust gas, removalequipment is necessary, and there are problems in terms of the operationand the environment.

It is an object of the present invention to solve the above-mentionedproblems, that is, to provide a method that, unlike the case in which anacidic gas is used, does not have problems in terms of the operation andthe environment, and that can continuously prevent a 2-cyanoacrylatefrom polymerizing in the distillate system when distilling the2-cyanoacrylate.

As a result of an intensive investigation in order to attain this objectby the present inventors into a method of preventing polymerization of a2-cyanoacrylate in the distillate system when distilling it, the presentinvention has been accomplished. That is, the present invention is amethod for producing a purified 2-cyanoacrylate by distilling a crude2-cyanoacrylate in the presence of a polymerization inhibitor,characterized in that a polymerization inhibitor having a boiling pointat normal pressure of within ±12° C. of the boiling point at normalpressure of the purified 2-cyanoacrylate is used as the polymerizationinhibitor.

BEST MODE FOR CARRYING OUT THE INVENTION

The present inventors have found that the polymerization inhibitor usedin JP-A-1-135754 has a boiling point that is higher than the boilingpoint of ethyl 2-cyanoacrylate by more than 12° C., and when apolymerization inhibitor having a boiling point that is higher than theboiling point of a 2-cyanoacrylate by more than 12° C. is used, the2-cyanoacrylate easily polymerizes in the distillate system. When thereason therefor was investigated, it was found that, although the use ofsuch a polymerization inhibitor can prevent polymerization in adistillation column for which its use is targeted, since thepolymerization inhibitor, as a vapor, does not accompany the2-cyanoacrylate, it cannot spread to the distillate system.

Furthermore, it has been found that the polymerization inhibitor used inJP-A4-124168 has a boiling point that is lower than the boiling point ofa 2-cyanoacrylate by more than 12° C., as is the case for a BF₃ ethercomplex salt or a BF₃ carboxylic acid complex salt, or has a boilingpoint that is higher than the boiling point of a 2-cyanoacrylate by morethan 12° C., as is the case for a BF₃ phenol complex salt, and when apolymerization inhibitor having a boiling point that is lower than theboiling point of a 2-cyanoacrylate by more than 12° C. is used,polymerization can easily occur in the distillate system in the latterhalf of the distillation during long term distillation. When the reasontherefor was investigated, it was found that such a polymerizationinhibitor separates in an initial stage of the distillation and goes outof the system. The present invention has been accomplished on the basisof the above-mentioned findings.

The present invention is explained in further detail below.

Examples of the 2-cyanoacrylate in the present invention include methyl2-cyanoacrylate, ethyl 2-cyanoacrylate, propyl 2-cyanoacrylate,isopropyl 2-cyanoacrylate, butyl 2-cyanoacrylate, isobutyl2-cyanoacrylate, amyl 2-cyanoacrylate, hexyl 2-cyanoacrylate, cyclohexyl2-cyanoacrylate, octyl 2-cyanoacrylate, 2-ethylhexyl 2-cyanoacrylate,allyl 2-cyanoacrylate, benzyl 2-cyanoacrylate, methoxyethyl2-cyanoacrylate, ethoxyethyl 2-cyanoacrylate, methoxypropyl2-cyanoacrylate, and tetrahydrofurfuryl 2-cyanoacrylate, and these2-cyanoacrylates may be used not only singly but also in a combinationof two or more types.

The boiling points of these 2-cyanoacrylates at normal pressure are forexample 195° C. for methyl 2-cyanoacrylate, 200° C. for ethyl2-cyanoacrylate, 205° C. for isopropyl 2-cyanoacrylate, and 210° C. forisobutyl 2-cyanoacrylate.

The polymerization inhibitor used in the present invention has a boilingpoint at normal pressure that is within ±12° C. of the boiling point atnormal pressure of a given purified 2-cyanoacrylate, and preferablywithin ±10° C. The actual distillation of a 2-cyanoacrylate is oftencarried out at reduced pressure. The difference in boiling point betweencompounds decreases under reduced pressure, but since the differencevaries according to the degree of reduced pressure, in the presentinvention the boiling points at normal pressure are used as the basis.As long as the above-mentioned conditions are satisfied, thepolymerization inhibitor used in the present invention may be a radicalpolymerization inhibitor, but an anionic polymerization inhibitor ispreferable.

Examples of the anionic polymerization inhibitor (figures in bracketsare based on the boiling point at normal pressure) include, with respectto ethyl 2-cyanoacrylate (200° C.), chloroacetic acid (189° C.),dichloroacetic acid (194° C.), trichloroacetic acid (196° C.),bromoacetic acid (206° C.), dibromofluoroacetic acid (198° C.),3-chloropropionic acid (203-205° C.), 2,2-dichloropropionic acid (210°C.), 2-bromopropionic acid (203° C.), 2-chlorobutyric acid (210° C.),4-chlorobutyric acid (196° C.), tert-butylacetic acid (190° C.),2,3-dimethylbutyric acid (191-192° C.), 2-ethylbutyric acid (191-195°C.), 2-ethyl-2-methylbutyric acid (200-202° C.), 3-methoxyisobutyricacid (197-201° C.), 2-methylvaleric acid (196-197° C.), 3-methylvalericacid (196-198° C.), 4-methylvaleric acid (199-201 ° C.), 2-ethylvalericacid (209° C.), 2-methoxyvaleric acid (193-197° C.), hexanoic acid (202°C.), 5-hexenoic acid (202° C.), 3,3-dimethylacrylic acid (194-195° C.),pentafluoropropanesulfonic acid (196° C.), a BF₃ methanol complex (200°C.), and a BF₃ ethanol complex (200° C.).

Furthermore, examples thereof include, with respect to propyl2-cyanoacrylate (210° C.), bromoacetic acid, 3-chloropropionic acid,2,2-dichloropropionic acid, 2-bromopropionic acid, 3-ethoxypropionicacid (216° C.), 3-ethoxy-2-methylpropionic acid (214-215° C.),2-chlorobutyric acid, 2-ethyl-2-methylbutyric acid, 3-methoxyisobutyricacid, 2-methoxymethylbutyric acid (218-220° C.), 2-ethylvaleric acid,2-ethyl-4-methylvaleric acid (218-220° C.), 2-propylvaleric acid (220°C.), hexanoic acid, 2-methylhexanoic acid (209° C.), 5-methylhexanoicacid (212° C.), 5-hexenoic acid, nonafluorobutanesulfonic acid (210-212°C.), a BF₃ methanol complex, and a BF₃ ethanol complex.

Moreover, examples thereof include, with respect to butyl2-cyanoacrylate (230° C.), 3-methylsulfanylpropionic acid (235-240° C.),2,2-diethylbutyric acid (220-221 ° C.), 2-methoxymethylbutyric acid,2-ethoxymethylbutyric acid (225-226° C.), 3,4-dimethylvaleric acid(220-225° C.), 2-ethyl-4-methylvaleric acid, 2-propylvaleric acid,5-oxovaleric acid (240° C.), 2,5-dimethylhexanoic acid (228-230° C.),heptanoic acid (223° C.), 3-ethylheptanoic acid (236° C.), octanoic acid(237° C.), cyclohexanecarboxylic acid (232-233° C.), trichloroacrylicacid (221-223° C.), cyanoacetic acid (230° C.),undecafluoropentanesulfonic acid (223-226° C.), andtridecafluorohexanesulfonic acid.

Furthermore, examples thereof include, with respect to ethoxyethyl2-cyanoacrylate (240° C.), 3-methylsulfanylpropionic acid, 5-oxovalericacid, 2,5-dimethylhexanoic acid, 3-ethylheptanoic acid,2-methoxyheptanoic acid (246-250° C.), octanoic acid, 2-methyloctanoicacid (244-246° C.), cyclohexanecarboxylic acid, and cyanoacetic acid.

Among these polymerization inhibitors, since those having a high acidityare fast-acting at low concentration, a halocarboxylic acid or ahalosulfonic acid is preferable. Specific examples thereof includechloroacetic acid, dichloroacetic acid, trichloroacetic acid,bromoacetic acid, dibromofluoroacetic acid, 3-chloropropionic acid,2,2-dichloropropionic acid, 2-bromopropionic acid, 2-chlorobutyric acid,4-chlorobutyric acid, pentafluoropropanesulfonic acid,nonafluorobutanesulfonic acid, trichloroacrylic acid,undecafluoropentanesulfonic acid, tridecafluorohexanesulfonic acid, and3-methylsulfanylpropionic acid. Furthermore, if the relationship to theboiling point of a 2-cyanoacrylate is satisfied, dichloroacetic acid andtrichloroacetic acid are particularly preferable. Moreover, other thanthe halocarboxylic acids and halosulfonic acids, a BF₃ methanol complexand a BF₃ ethanol complex are preferable.

These boiling points can be looked up in a catalogue such as Aldrich ora chemical database called ‘CrossFire Beilstein’.

With regard to the crude 2-cyanoacrylate used in the present invention,a crude 2-cyanoacrylate that can be obtained by a standard method inwhich, for example, a cyanoacetic acid ester and formaldehyde are heatedand condensed in an organic solvent in the presence of a basic catalyst,and the condensate thus obtained is depolymerized at reduced pressureand high temperature in the presence of a depolymerization catalyst anda polymerization inhibitor, may generally be used.

With regard to a distillation method, there is, for example, a method inwhich the crude 2-cyanoacrylate produced by the above-mentioned methodis heated at reduced pressure using a packed distillation column or aplate-type distillation column. During this process, the distillationpressure is preferably 1 to 10 mmHg, and the distillation temperature ispreferably 50° C. to 100° C.. Furthermore, during this process, it ispreferable to add, to the crude 2-cyanoacrylate in the vessel, ananionic polymerization inhibitor such as diphosphorus pentoxide,paratoluenesulfonic acid, methanesulfonic acid, or propanesultone or aradical polymerization inhibitor such as hydroquinone, t-butylcatechol,or pyrogallol, and it is more preferable to add both thereof. Sincethese polymerization inhibitors are added for stabilization of a vesselsolution, it is preferable to use one having a boiling point that ishigher than the boiling point of a target 2-cyanoacrylate by more than12° C. The amounts of anionic polymerization inhibitor and radicalpolymerization inhibitor having boiling points that are higher than theboiling point of the 2-cyanoacrylate by more than 12° C. are preferably0.05 to 1.0 parts by weight for either of the polymerization inhibitorsrelative to the 2-cyanoacrylate (100 parts by weight).

With regard to a method of adding a polymerization inhibitor having aboiling point that is within ±12° C., and preferably ±10° C., of theboiling point of a 2-cyanoacrylate, it may be added to a crude2-cyanoacrylate in a vessel in advance, or it may be dissolved in apurified 2-cyanoacrylate and added to a distillation vessel orcontinuously added via an upper part of a distillation column. It ispreferable that the polymerization inhibitor is added to the vessel andcontinuously added via the upper part of the distillation column.

The polymerization inhibitor is preferably added in an amount of 1 to1000 wt ppm relative to the crude or purified 2-cyanoacrylate, and morepreferably 10 to 100 wt ppm. If the polymerization inhibitor is in theabove-mentioned range, it exhibits a sufficient effect as apolymerization inhibitor, there is no possibility that it might undergopolymerization within the distillate system, and the adhesion speed ofthe fraction obtained can be maintained at the intended speed.

It is preferable for the purpose of storage to add to the distilledpurified 2-cyanoacrylate an appropriate amount of an anionicpolymerization inhibitor such as SO₂, paratoluenesulfonic acid,methanesulfonic acid, propanesultone, or a BF₃ complex, or a radicalpolymerization inhibitor such as hydroquinone, t-butylcatechol, orpyrogallol.

It is surmised that the reason why, in the distillation of a2-cyanoacrylate, polymerization in the distillate system can beprevented if a polymerization inhibitor having a boiling point that isclose to that of the 2-cyanoacrylate is used is because thispolymerization inhibitor accompanies the 2-cyanoacrylate vapor to thusspread evenly from the distillation column to the distillate system, andpolymerization can therefore be prevented throughout the distillationequipment over a long period of time.

EXAMPLES

The present invention is explained in further detail by reference toExamples and Comparative Examples, but the present invention is notlimited thereby. As an evaluation method, the presence or absence of apolymer in the distillate system was visually examined.

Examples 1 to 6 and Comparative Examples 1 to 4

Hydroquinone (0.5 wt %) and diphosphorus pentoxide (0.1 wt %) were addedto crude ethyl 2-cyanoacrylate as vessel solution stabilizers, themixture was refluxed using a packed distillation column having atheoretical number of plates of 10 at a reduced pressure of 5 mmHg andat a vessel temperature of 70° C. to 80° C. for 1 hour whilecontinuously spraying a purified ethyl 2-cyanoacrylate solution of acompound shown in Table 1 as a polymerization inhibitor (theconcentration being shown in Table 1) from an upper part of the packedcolumn, then distilled at a reflux ratio of 3. After an initial fractionof 10% was distilled away, a fraction of 60% to 70% of purified ethyl2-cyanoacrylate was obtained. The presence or absence of polymerizationin the distillate system is shown in Table 1.

Example 7

Hydroquinone (0.5 wt %) and diphosphorus pentoxide (0.1 wt %) were addedto crude methyl 2-cyanoacrylate as vessel solution stabilizers,distillation was carried out in the same manner as in Example 1 exceptthat a purified methyl 2-cyanoacrylate solution of a compound shown inTable 1 as a polymerization inhibitor (the concentration being shown inTable 1) was continuously sprayed from an upper part of the packedcolumn, and purified methyl 2-cyanoacrylate was obtained. The presenceor absence of polymerization in the distillate system is shown in Table1.

Example 8

Hydroquinone (0.5 wt %) and diphosphorus pentoxide (0.1 wt %) were addedto crude isopropyl 2-cyanoacrylate as vessel solution stabilizers,distillation was carried out in the same manner as in Example 1 exceptthat a purified isopropyl 2-cyanoacrylate solution of a compound shownin Table 1 as a polymerization inhibitor (the concentration being shownin Table 1) was continuously sprayed from the top of the packed columnand the vessel temperature was 80° C. to 90° C., and purified isopropyl2-cyanoacrylate was obtained. The presence or absence of polymerizationin the distillate system is shown in Table 1.

Example 9

Hydroquinone (0.5 wt %) and diphosphorus pentoxide (0.1 wt %) were addedto crude isobutyl 2-cyanoacrylate as vessel solution stabilizers,distillation was carried out in the same manner as in Example 1 exceptthat a purified isobutyl 2-cyanoacrylate solution of a compound shown inTable 1 as a polymerization inhibitor (the concentration being shown inTable 1) was continuously sprayed from an upper part of the packedcolumn and the vessel temperature was 80° C. to 90° C., and purifiedisobutyl 2-cyanoacrylate was obtained. The presence or absence ofpolymerization in the distillate system is shown in Table 1. TABLE 1Polymerization inhibitor 2-Cyanoacrylate Boiling Polymer in Boilingpoint Amount distillate Type point (° C.) Type (° C.) added* system Ex.1 Ethyl 200 Dichloroacetic acid 194 50 None Ex. 2 Ethyl 200Dichloroacetic acid 194 10 None Ex. 3 Ethyl 200 Dichloroacetic acid 194100 None Ex. 4 Ethyl 200 Trichloroacetic acid 196 10 None Ex. 5 Ethyl200 Hexanoic acid 202 100 None Ex. 6 Ethyl 200 BF₃ methanol complex 20050 None Ex. 7 Methyl 195 Dichloroacetic acid 194 50 None Ex. 8 Isopropyl205 BF₃ methanol complex 200 50 None Ex. 9 Isobutyl 210 Bromoacetic acid206 100 None Comp. Ex. 1 Ethyl 200 Paratoluenesulfonic acid 260 50 Yes(large amount) Comp. Ex. 2 Ethyl 200 4-Methylhexanoic acid 221 100 Yes(large amount) Comp. Ex. 3 Ethyl 200 BF₃ diethyl ether complex 126 50Yes (large amount) Comp. Ex. 4 Ethyl 200 BF₃ acetic acid complex 180 50Yes (small amount)*ppm

As is clear from Table 1, when the polymerization inhibitor inaccordance with the present invention was not used but a polymerizationinhibitor having a boiling point that was higher than the boiling pointof the 2-cyanoacrylate by more than 12° C. was instead added(Comparative Example 1 and 2), and when a polymerization inhibitorhaving a boiling point that was lower than the boiling point of the2-cyanoacrylate by more than 12° C. was instead added (ComparativeExample 3 and 4), a polymer deposit was observed on the distillatesystem during distillation. In contrast, when a polymerization inhibitorwas continuously added by the method in accordance with the presentinvention (Examples 1 to 9), no polymer deposit was observed on thedistillate system.

INDUSTRIAL APPLICABILITY

The present invention enables polymerization in a distillation columnand a distillate system to be prevented continuously, even whendistillation of a 2-cyanoacrylate is carried out for a long period oftime, by carrying out distillation in the presence of a polymerizationinhibitor having a boiling point that is within ±12° C. of the boilingpoint of the 2-cyanoacrylate. In accordance with the present invention,a purified 2-cyanoacrylate having a high purity can be obtained in onestep by carrying out distillation using, for example, a multi-platedistillation column or by increasing a reflux ratio.

1. A method for producing a purified 2-cyanoacrylate by distilling acrude 2-cyanoacrylate in the presence of a polymerization inhibitor,characterized in that a polymerization inhibitor having a boiling pointat normal pressure of within ±12° C. of the boiling point at normalpressure of the purified 2-cyanoacrylate is used as the polymerizationinhibitor.
 2. The production method according to claim 1, wherein thepolymerization inhibitor is an anionic polymerization inhibitor.
 3. Theproduction method according to claim 2, wherein the anionicpolymerization inhibitor is a halocarboxylic acid or a halosulfonicacid.
 4. The production method according to claim 3, wherein thehalocarboxylic acid or the halosulfonic acid is chloroacetic acid,dichloroacetic acid, trichloroacetic acid, bromoacetic acid,dibromofluoroacetic acid, 3-chloropropionic acid, 2,2-dichloropropionicacid, 2-bromopropionic acid, 2-chlorobutyric acid, 4-chlorobutyric acid,pentafluoropropanesulfonic acid, nonafluorobutanesulfonic acid,trichloroacrylic acid, undecafluoropentanesulfonic acid,tridecafluorohexanesulfonic acid, or 3-methylsulfanylpropionic acid. 5.The production method according to claim 2, wherein the anionicpolymerization inhibitor is a BF₃ methanol complex or a BF₃ ethanolcomplex.
 6. The production method according to claim 1, wherein thepolymerization inhibitor is added to a vessel in advance.
 7. Theproduction method according to claim 1, wherein the polymerizationinhibitor is dissolved in a purified 2-cyanoacrylate and continuouslyadded via an upper part of a distillation vessel or an upper part of adistillation column.
 8. The production method according to claim 6,wherein the polymerization inhibitor is added at 1 to 1000 wt ppmrelative to the crude 2-cyanoacrylate.
 9. The production methodaccording to claim 7, wherein the polymerization inhibitor is added at 1to 1000 wt ppm relative to the crude 2-cyanoacrylate.
 10. The productionmethod according to claims 1, wherein a crude 2-cyanoacrylate obtainedby heating and condensing a cyanoacetic acid ester and formaldehyde inan organic solvent in the presence of a basic catalyst, anddepolymerizing the condensate thus obtained in the presence of adepolymerization catalyst and a polymerization inhibitor at reducedpressure and high temperature is used as the crude 2-cyanoacrylate. 11.The production method according to claims 1, wherein distillationemploys a method in which heating is carried out at reduced pressureusing a packed distillation column.
 12. The production method accordingto claims 1, wherein distillation is carried out by further adding, to a2-cyanoacrylate in a vessel, an anionic polymerization inhibitor and aradical polymerization inhibitor that have a boiling point that ishigher than the boiling point of the 2-cyanoacrylate by more than 12° C.13. The production method according to claim 12, wherein the anionicpolymerization inhibitor is phosphorus pentoxide and the radicalpolymerization inhibitor is hydroquinone.